It is now generally accepted that osteoporosis of adulthood is a heterogeneous condition, some of which may represent a failure of normal osteogenesis during childhood and adolescence. This grant will develop the methodologies to ultimately test whether asymptomatic childhood osteoporosis can be identified and shown to lead to clinically significant bone disease in adult life. The method is based on safe non-invasive tests which assess bone mass - single and dual beam photon absorptiometry (SBPA and DBPA) - and allow for serial measurements of cortical and trabecular bone. Using these two techniques, we will establish normative cross-sectional standards for bone mineral of the forearm and spine in normally growing children. These data will for the first time correlate cortical and trabecular bone measurements with each other and with standard clinical measures of growth and pubertal development. Subjects with Turner's syndrome will be studied as an example of childhood osteopenia. Cross-sectional bone density data will be obtained on Turner's patients of all ages to define the changes in bone mass that occurs with age in this disorder. This information will give insight into the changes of the appendicular and axial skeleton with age in a condition characterized by diminished osteogenesis. A subset of these subjects will be serially monitored by SBPA and DBPA prior to and during long-term hormonal therapy designed to enhance both linear growth and bone density. This data will judge the efficacy of therapy and determine if the effect on cortical and trabecular bone is concordant. As a unit, these studies will form the basis for identifying other groups of children known to be at increased risk for inherited or metabolic bone disease and for instituting and monitoring therapeutic regimens aimed at achieving optimal bone mineral accretion.